Mammalian spermatogenesis is a hormone-dependent process regulated mainly by follicle stimulated hormone (FSH) and testosterone (T). The effects of these hormones on germ cell (Gc) differentiation are believed to be indirect mediated through the somatic Sertoli cells (Sc). Although T and/or FSH were shown to influence various Sc functions, including secretion of several specific proteins (e.g., androgen binding protein, inhibin, transferrin, plasminogen activator, the mechanism by which the Sc mediate hormonal effects on the Gc is not known. The overall objective of this proposal is to clarify the Sc-Gc interaction by exploring a hypothesis that certain critical products required by the Gc during their differentiation are produced by the Sc and transferred to the Gc. The specific aims are: 1) to define culture conditions for optimal maintenance of spermatogenesis in vitro; 2) to determine whether some prelabeled Sc products (proteins, glycoproteins or RNA) are transferred to the Gc during certain specific stages of differentiation, by using tissue culture, radioautography and scintillation count methods; 3) to explore the effects of FSH and T on the secretion and transfer of these substances; 4) to examine a possible correlation between the transfer of these Sc products and Gc differentiation; and, 5) attempt to characterize the chemical nature of the transferred Sc products by using various immunologic (RIA, immunoprecipitation, immunofluorescence) and biochemical (two-dimensional gel electrophoresis, Western blots, HPLC, etc.) methods. These studies may provide valuable information on the mechanism by which hormones regulate spermatogenesis.